Prebaked carbon anodes and anode assembly for the production of aluminum



Aug. 20, 1968 R. BONFILS ETAL 3,398,081

PREBAKED CARBON ANODES AND ANODE ASSEMBLY FOR THE PRODUCTION OF ALUMINUM Filed April 5. 1966 4 Sheets-Sheet 1 INVE/VTGQJ Ps/ve BOW/71.8

Aug. 20, 1968 R. sour-11.5 ETAL 3,398,081

PREBAKED CARBON ANODES D ANODE ASSEMBLY FOR THE PR NUM ODUCTIO F ALUMI Filed April 5. 1966 4 Sheets-Sheet 2 Aug. 20, 1968 FEB ONFILS E BAKED CARBON ANOuES AND ANODE ASSEMBLY 3,398,081 FOR Filed April 5. l9

20. 1968 R.BONFILS ETAL 3,393,081

PREBAKED CARBON ANODES AND ANODE ASSEMBLY FOR THE PRODUCTION OF ALUMINUM Filed April 5. 1966 4 Sheets-Sheet 4 6 i g5 l k i i I f I 7 I I & I 1 l 6 Z a A IQ 1' 1 4/// //////v/fl/ww/flfl/fliva FIG. 6

United States Patent 3,398,081 PREBAKED CARBON ANODES AND ANOD ASSEMBLY FOR THE PRODUCTION OF ALUMINUM Ren Bonfils andHeuri Des Rochettes, St. Jean-de- Maurienne, France, assignors to Pechiney-Compagnie de Produits Chimiques et Electrometallurgiques, Paris,

' France Filed Apr. 5, 1966, Ser. No. 540,254 8 Claims. (Cl. 204-286) This invention relates to the manufacture of prebaked carbon electrodes andrelates more particularly to a new and improved prebaked carbon anode adapted for use in the preparation of aluminum by electrolytic technique from a molten bath.

In practice, the prebaked anode is suspended from the positive frame of an electrolytic tank with the lower portion of the anode immersed in the electrolyte. For purposes of interconnecting the anode with the frame, for support of the anode while maintaining an electrically conductive relationship therebetween, the anode is molded with cavities in the upper end for receipt of feet on the lower end of a stem by which the assembly is suspended from the tank. u 7

It is desirable to effect a good seal between the feet and the anode to maintain a good electrical conductive relationship therebetween. For this purpose, the space remaining between the feet, when inserted into the cavity, is filled with a conductive material of high strength, such as cast iron. l

The cast iron solidifies as it cools and makes the desired mechanical and electrical bond between the carbon anode and the steel feet. When the anode is used up, it is withdrawn from the bath and the anode feet are recovered by a cast iron removal operation which relies upon the more brittle character of the cast iron to enable breakage from the feet in response to impact. Generally, the anode foot is in the form of a cylindrical bar which extends into the cavity formed in the upper end of the anode. The steel foot is of such mechanical strength as to resist breakage during the cast iron removal process. Anode feet of elongated form have also been tried but their resistance to the cast iron removal process has been found to be inadequate. l p

From the standpoint of electrical connection, a substantial voltage drop occurs between the carbon anode and the cast iron. From the standpoint of the mechanical connection, breaks in the seal of the anode, referred to as seal breakages, occur fairly frequently and, on such' occurrences, the anode drops into the bath.

Attempts have been made to rectify these drawbacks by forming the cavity with vertical or helical grooves which extend from the'top to the bottom of the lateral wall of the cavity to increase the area of contact between the anode and the cast iron. For the formation of such helical grooves, the cavities are formed of dies having ribs formed along a vertical axis about which the dies can rotate during removal of the anode from the mold.

It is an object of this invention to produce and to provide a method for producing a new and improved electrode which overcomes many of the difiiculties heretofore encountered, which minimizes the voltage'drop at the sealing level and it is a related object to produce a carbon electrode and elements employed in combination therewith to produce an assembly which gives an improved performance especially. in the manufacture of aluminum by electrolysis.

Another object is to produce a prebaked carbon electrode having improved electrical and mechanical connection to the anode feet and in which a good electrical and mechanical connection is maintained substantially throughout the period of use tion of aluminum.

A further object is to produce a mold for use in shap ing prebaked carbon anodes wherein the mold comprises a die, preferably movable, which includes a core formed to provide grooves of trapezoidal (swallowtail) profile in the side walls of the formed cavity.

These andother objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments ofthe invention are shown in the accompanying drawings in which:

FIGURE 1 is a sectional view of 'an anode assembly which is representative of present practice, taken along the line Y-Y' of FIGURE 2;

FIGURE 2 is-a sectional view taken alongthe line XX of FIGURE 1; e

FIGURE 3 is a sectional view take X1X1' Of FIGURE 4 is a corresponding sectional view taken along the line X -X of FIGURE 1 when the anode is constructed in accordance with the practice of this invention;

FIGURE 5 is a sectional view taken along the line X -X of FIGURE 1 when the anode embodies the features of this invention; and,

FIGURE 6 is a vertical sectional view of the cavity formed in an anode embodying the features of this invention. 1

In the drawing, the numeral 1 represents the prebaked carbon anode, 2 is the cavity formed in the upper end of the anode, 3 the cast iron sealing material, 4 the foot on the lower end of the cylindrical bar of steel and 5 is the anode rod. The numeral 6 represents the grooves formed in the side walls of the cavity. 1

It will be seen by comparison between the horizontal cross section of the cavity at the top in FIGURE 4 and at the bottom in FIGURE 5 that the groove 6 is of helical form i.e., helical grooves inclined at an angle of about 18 in the drawing, as shown in FIGURE 6.

As shown in FIGURES 4 and 5, the sides of the grooves may be extended to form a substantially isosceles triangle ABC having an apex angle a. FIGURES 4 and 5 have been placed one above the other more clearly to illustrate the relationship between the grooves at the upper portion of the cavity by comparison with the shape of the grooves farther down and particularly the back-off existing be-. tween the top and bottom of each groove. Likewise, the lower part of FIGURE 4 has been shown below FIGURE 6 more clearly to illustrate the inclination of the grooves with respect to the vertical, that is to say, their helical nature.

The object of the invention resides in the improvement in prebaked carbon anodes intended for the production of aluminum by igneous electrolysis in which at least one cavity is provided in the upper portion of each anode for sealing the prebaked anode to the metal foot of the sup porting stem. Each cavity is provided on its side wall with gnooves 6 extending from the top Otf the bottom and in which the grooves are of trapezoidal shape, such as a swallowtail profile whereby, upon cooling the sealing cast iron, at squeezing or gripping action is effected against the walls of the cavity. I In accordance with a particular embodiment of the invention, the profile of the grooves is adapted to define a substantially isosceles triangle in which the apex angle a is selected to be within the range of 20 to 60 and preferably within the range of 30 to 50.'-Inaccordance with another feature of this invention, the groove is in the form of a helical groove in which the apex angle diminishes from the top to the bottom of the groove. In other words, there is a considerable back-off, generally within the range of 5 to 10, between the top and bottom of of the anode in the producalong the line thegroovea fili ladvan gc otrhistarrangement isto. faciii---.-

tate removal of the die and to diminish or even nullify the possibility of tearing the threads or removing portions ofthe sidewalls ofthe groove during mold stripping.

' The -angle of inclination of the groove with respect to particularly well adapted to the form of the anode and the vertical is generally within the range of 15 to 20. forallowing'regular and uniform distribution of current Forexarnple, the angle -is 18 in the modification which passing fromthe-castironiseal to the carbon anode. is, shown in FIGURES 4, 5 and 6. The angle at the apex The invention has been found to be particularly easy q o fthe substantially isosceles triangle ABC, formed by a'ridecOnomical in application.The press for making the the extension of the groove, is 46 at the upper portion anodesdilfers littl tromt t enal p fefss l x ep of .the impression (see FIGURE 4) and 40 at the botfor the 'shapeo'f'the die used to produce thecavity. In additom portion (see FIGURE 5, corresponding to aback-01f 6011, the nv n i makes. i pa tq u e f ode of-.6). Ihe foregoing is given by way of illustration and f f Substantial d mensionso. as to enable impacting not by way of limitation, i to remove the cast iron seal without damage thereof. 1 One of the importantimprovements of this invention .l e understeedthat v hg m y be made in resides iii-the increase-incontact area-between the cast t ils f c n tr cti n, arrangement and operation iron sealing material and the carbon wall of the anode Without departinafrom the Spirit O invention p al y thereby to improve the electric-a1 and mechanical contact. l e i the f w ng elaims- Other advantages include ease of removal of the dies W ai g 1 without damage oflthe threads or grooves when the anode p a e h h having a v y in the imprint die is removed from the anode to leave the cor PP en p n for receiving an anode toot for di cavity; A d of hi d h i l tachment thereto in which the cavity is formed with helicalstrength are produced thereby to minimize and practically grooves extending d w w y from the upper el'id-lof li i instances of anode seal breakages i the cavity in the side walls thereof and in which the side Moreover, because of the trapezoidal (swallowtail) so the groove h i of trapezoidal l-7 shape of the grooves, as the cast iron used for sealing A p a eal'hoh a as claimed in claim 1 shrinks upon cooling, a squeezing effect takes place which in which the 'grooyes eXtehd continuously from the P enhances contact with the anode. By virtue of this squeezof cavity to the bottom ing effect; the electrical contact between the carbon anode A P eba earboh a e as claimed in claim 1 and the sealing castiron is greatly improved. More parf h. heheeldal grooves have an angle of inclinaticularly, prebaked anodes, prepared in accordance with tloh Wlthlh the range t0 1-. the-practice of this invention, do not give rise to ab- 4! Ahahode assembly comprising the ehmhihattoh of normal voltage drops between the carbon anode and the the Pt k carbon ahOde Claimed in claim an anode casti even during the early stages f use stern, a foot on the lower end of the anode stem which 'In the following table, comparison is made of the voltextends Into the cal/1W, e hen filling the Space age drop between anodes prepared according to. the prior t ee the e t h the h Walls of h f y t0 ettect state of art, is represented by FIGURES 1, 2 and 3 and h& 9 5 P r e w e nd Whlch. h cast anodes prepared in. accordance withthe practice of this 0115111165265 h h-? d.e In response 3 invention, as represented by FIGURES 4, 5 and 6. The h h F e g sohdlficatlhh of the st n voltage drop measurement is taken between the cast iron 0 poure Into t eavltyto fill the P sealing material andthe bottom of the anode. The voltp ba e carbon anode as claimed in Claim 1 age drop readings were made on the days set forth in the n w e e e extended, define a b table. The current densitywas 0.75 amps per square crn. ye s trlangle m an p angle within the under the anode. The thickness of the carbon in the new rahge Q to anode between the sealing cast iron was approximately A pfehaked'eafhoh anode as claimed in Claim 5 in 43 cm. After 23 days of use, the anode was removed from w h t p angle is Within the R g Of to thc bath'of electrolyte and the thickness of carbon below 7. A prebaked carbon anode as claimed in claim 1 in the cast iron was no more than 1 cm. which the apex angle at the top of the grooves is greater 2nd 3rd 5th 10m 15m 20th 23rd day day day day day day day According to the prior state of 1 ear 0.35 0.33 0.30 0.25 0.20 0.17 0.15 According to-thainvention..- 0.27 0. 23 0.19 0.13 0. 09 0. 09 0. 05

. It will be seen from the'foregoing example that the than the apex angle in the" lower portions of the groove. average voltage gain is 0.1 volt as compared to the con- 1A Prebaked eafbonanede as Cl Cla m 7 in ventional method. This represents a gain of 350 kw./ hr. Which'the 'haekotf h e' P angle at the p the per metric ton of aluminum produced for consumption of apex angle at the bottom 15 Wlthlh the range of 5 to l5,000 kw./hour per metric ton. f Ct As previously pointed out, the mechanical strength of v e erences e the carbon anode-cast iron connection is greatly improved UN S A ES PATENTS whereby the frequency of anode seal breakages is mark- 1,467,060 9/1923 Munning 204 288 edl-y reduced as demonstrated by the following. In a series 2,769,113 10/ 1956 r Graybeal 204286 XR of 104 commercial tanks, each containing 28 prebaked 2,93 9,829 6/1960 Allen 204-243 anodes, the number of seal breakages prior to the practice 3,25 8,416. 1966 Mantovanello 204-280 of this invention was an average of 7.5 daily. The anodes 14,044 -4/ 1967 Powell 287126 XR of this invention were gradually introduced into the commercial practice with the result that the number of seal breakages dropped rapidly and averaged only 07 anode HOWARD SQ V VILLIAMS, Primary Examiner. U D; R. JORDAN, Assistant Examiner. 

1. A PREBAKED CARBON ANODE HAVING A CAVITY IN THE UPPER END PORTION FOR RECEIVING AN ANODE FOOT FOR ATTACHMENT THERETO IN WHICH THE CAVITY IS FORMED WITH HELICAL GROOVES EXTENDING DOWNWARDLY FROM THE UPPER END OF 